1. Field of the Invention
The present invention relates to a Method and Apparatus for Electro Chemical Mechanical Deposition, and more particularly, to a method and apparatus that provides for both the deposition and polishing of a conductive material on a semiconductor wafer.
2. Background of the Invention
Metallization of semiconductor wafers, i.e. deposition of a layer of metal on the face of wafers over a barrier/seed layer of metal has important and broad application in the semiconductor industry. Conventionally, aluminum and other metals are deposited as one of many metal layers that make up a semiconductor chip. More recently, there is great interest in the deposition of copper for interconnects on semiconductor chips, since, as compared to aluminum, copper reduces electrical resistance and allows semiconductor chips using copper to run faster with less heat generation, resulting in a significant gain in chip capacity and efficiency.
Conformal thin film deposition of copper into deep submicron via holes and trenches is becoming more difficult in ULSI chip processing, especially when the feature sizes are decreasing below the 0.25 μm with aspect rations of greater that 5 to 1. Common chemical vapor deposition and electroplating techniques have been used to fill these deep cavities etched into silicon substrates. These processes so far have yielded a very high cost and defect density for developing and integrating local interconnects for ULSI technology.
One of the factors that contributes to the high cost is the manner in which the conductive material, and particularly copper, is applied, Specifically, it is well known to apply certain contaminants, known as leveling agents, in the electrolyte solution that prevent or slow down the rate of deposition of the metal to the surface of the wafer substrate. Since these contaminants have a large size in comparison to the size of the typical vie that needs to be filled, deposition of the metal on the surface of the wafer is, in part, prevented. This prevention, however, is achieved at the expense of adding contaminants to the electrolytic solution, which results, in part, in vias that do not have the desired conductive characteristics. In particular, the grain size of the deposited conductor, due to the use of such contaminants, is not as large as desired, which thereby results in quality problems for the resulting device, as well as increased expense due to significant annealing times that are subsequently required.
Further, the cost of achieving the desired structure, in which the conductive material exists in the via, but not on the substrate surface, still required separate deposition and polishing steps. After the conventional deposition of the metal using an anode, a cathode and electrolytic solution containing metal as is known, there is then required a polishing step, which polishing step is, for high performance devices at the present time, typically a chemical-mechanical polishing step. While chemical mechanical polishing achieves the desired result, it achieves it at considerable expense, and requires a great degree of precision in applying a slurry in order to achieve the desired high degree of polish on the conductive surface.
Accordingly, a less expensive and more accurate manner of applying a conductor to a semiconductor wafer is needed